Biology subjects

Polat, A.

Publications and source records attributed to Polat, A..

2 recordsLinked to original sources

bioRxiv2026

Low-salt diet induces claudin-3 expression and drives adaptive changes in collecting duct of claudin-3-deficient mice

BackgroundRenal sodium reabsorption occurs via both transcellular and paracellular pathways. Tight junction proteins play a key role in mediating paracellular transport. The collecting duct (CD) is critical for the fine-tuning of Na+ balance and is sensitive to changes in dietary salt intake. A low-sodium diet, which increases endogenous aldosterone secretion, stimulates transcellular sodium transport via epithelial Na+ channels (ENaC) and Na,K-ATPase. We hypothesized that a low-sodium diet also modulates paracellular Na+ permeability by regulating the expression or function of claudin-3, a major tight junction protein in the CD, in order to limit the back-leak of reabsorbed sodium and preserve sodium balance. MethodsWe used in vivo mouse models and cultured mouse CD principal cells (mCCDcl1) to assess aldosterones effects on tight junction proteins. In mCCDcl1 cells, aldosterone-induced changes in claudin-3 expression and localization were evaluated via Western blotting and immunofluorescence, and Ussing chamber assays were used to assess paracellular Na+ and Cl- permeability after modulating claudin-3 expression. Wild-type and claudin-3 knockout mice were fed low (0.01%) or normal (0.18%) sodium diets for seven days. In subsets of low sodium diet mice, spironolactone (a mineralocorticoid receptor antagonist) was administered. ResultsIn mice, a low-sodium diet upregulates renal claudin-3 expression. Concordantly, in vitro studies using mCCDcl1 cells showed that aldosterone treatment increased claudin-3 protein levels and promoted its localization to the lateral membrane. Functional analyses demonstrated that claudin-3 overexpression reduced paracellular permeability to both Na+ and Cl-, while claudin-3 silencing increased it. Claudin-3 knockout mice subjected to a low-sodium diet exhibited compensatory upregulation of the - and {gamma}-subunits of ENaC, alongside increased expression of claudin-4, claudin-8, and claudin-10. This highlights an adaptive response that maintains sodium homeostasis in the absence of claudin-3. Importantly, this compensatory mechanism persists even under spironolactone treatment, suggesting that the adaptation of claudin-3-deficient mice occurs independently of mineralocorticoid receptor activation. ConclusionsOur findings demonstrate that aldosterone enhances claudin-3 expression, reinforcing the paracellular barrier to Na+ and complementing its classical role in transcellular Na+ transport. Under low-sodium conditions, claudin-3-deficient mice adapt through complementary mechanisms aimed at increasing sodium reabsorption via ENaC activation and upregulation of claudin-4 and claudin-8, both barrier-forming claudins that restrict paracellular sodium leakage in the CD. This is associated with increased claudin-10 abundance in the thick ascending limb of Henle, a pore-forming claudin that facilitates paracellular sodium permeability. This study advances our understanding of the complex control of renal sodium handling, revealing adaptive mechanisms in response to low-salt diet and claudin-3 deficiency.

physiology↗

bioRxiv2020

The urban-adapted underground mosquito, Culex molestus, maintains exogenously influenced circadian rhythms despite an absence of photoperiodically induced dormancy

In temperate climates, the mosquito Culex molestus lives almost exclusively in urban underground locations such as flooded basements, sewer systems and subway tunnels. Unlike most other mosquito taxa found at higher latitudes, Cx. molestus remains active and continues to breed throughout the winter. This is attributable to year-round above freezing temperatures in its preferred underground habitats combined with an inability to enter a state of arrested development ( diapause) in response to shortening photoperiods in autumn. Prior studies have shown that the genes associated with circadian rhythms (i.e. clock genes) also influence the photoperiodic induction of diapause in the closely related mosquito, Cx. pipiens. These results suggest that molecular changes in one or more clock genes could contribute to the absence of photoperiodically induced diapause in Cx. molestus. As Cx. molestus predominantly inhabits underground locations generally devoid of a predictable photoperiod, such mutations may not be removed by purifying selection as they would have minimal fitness consequences. To examine the possibility that Cx. molestus- specific genetic changes in one or more clock genes correlate with its inability to enter a photoperiodically induced dormant state, we first used genomic data to search for inactivating mutations or other structural variants in genes known to influence circadian rhythms in Diptera ( flies). We further investigated non-synonymous, derived genetic divergence in this same class of genes. Next, we generated transcriptome data from multiple life-stages of Cx. molestus to survey binary expression of annotated clock genes throughout this mosquitos lifecycle. Finally, we carried out experimental studies to assess the extent to which Cx. molestus retains exogenously influenced circadian rhythms, and whether it harbors any tendencies towards dormancy when exposed to a shortened photoperiod. Our results indicate that the gene Helicase domino (dom) has a nine-nucleotide, in-frame deletion specific to Cx. molestus. Previous work has shown that splice variants in this gene influence circadian behavior in Drosophila melanogaster. We also find derived, non-synonymous single nucleotide polymorphisms (SNPs) in eight genes that may also affect circadian rhythms and/or diapause induction in Cx. molestus. Four other circadian genes were found to have no quantifiable expression during any examined life stage, suggesting potential regulatory variation. Our experimental results confirm that Cx. molestus retains exogenously-influenced circadian rhythms but is not induced to enter a dormant state by a shortened photoperiod. Collectively, these findings show that the distinct, but potentially molecularly interconnected life-history traits of diapause induction and circadian rhythms are decoupled in Cx. molestus and suggest that this taxon may be a valuable tool for exploring exogenously influenced phenotypes in mosquitoes more broadly.

evolutionary biology↗